This application is based on Japanese Patent Application No. 2001-242629 filed on Aug. 9, 2001, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a vibration absorbing rubber hose, and more particularly to a rubber hose which is capable of exhibiting an excellent vibration absorbing characteristic and suitably used as a conduit or piping for a cooler or an air conditioner in an automotive vehicle.
2. Discussion of Related Art
A hose for transporting a refrigerant such as a flon gas is used as a conduit or piping for a cooler or an air conditioner in an automotive vehicle. In order to prevent a leakage flow of the refrigerant such as the flon gas having a low molecular weight through the hose and minimize environmental contamination, a hose of resin-rubber composite type having a laminar structure is mainly used as such a refrigerant transporting hose. The hose of resin-rubber composite type includes, as an innermost layer or an intermediate layer thereof, at least one resin layer formed of a resin material such as polyamide resin capable of exhibiting excellent gas impermeability.
The hose of resin-rubber composite type described above, however, has a low degree of flexibility or a high degree of rigidity of the resin layer, so that the vibrations generated during operations of the air conditioning system (including a compressor) and the internal combustion engine are transmitted via the hose to the components of the air conditioning system and the vehicle body. Accordingly, the hose of resin-rubber composite type described above does not exhibit a satisfactory vibration absorbing characteristic to reduce sound or noise which arises from the generated vibrations. Thus, the hose is generally required to exhibit a sufficiently high degree of flexibility and an excellent vibration absorbing characteristic. In particular, a low-pressure hose for transporting the refrigerant is desirably formed as a rubber hose consisting of at least one rubber layer and at least one reinforcing layer, without including the resin layer, for thereby considerably increasing the flexibility of the hose and assuring a satisfactory resistance to permeation of the refrigerant.
In JP-A-2-80880 and JP-A-3-140688, there is proposed a refrigerant transporting hose which does not have the resin layer as a barrier layer for preventing the refrigerant from permeating through the hose. Described in detail, the proposed refrigerant transporting hose is formed as a rubber hose having a laminar structure including an inner rubber layer, a reinforcing fiber layer formed of a suitable fiber, and an outer rubber layer, which layers are laminated integrally on one another in the order of description in the radially outward direction of the hose. The inner rubber layer is formed of a butyl rubber or a halogenated butyl rubber, which exhibits a high degree of resistance to permeation of 1,1,1,2-tetrafluoroethane (HFC134a) as one example of the flon gas, while the outer rubber layer is formed of an ethylene-propylene-diene rubber (EPDM) or a chloroprene rubber (CR). The thus formed conventional rubber hose without the resin layer as the barrier layer, however, is not satisfactory in terms of its vibration absorbing characteristic.
The rubber hose is required to exhibit the desired vibration absorbing characteristic over a wide range of temperature in which the rubber hose is used. The low-pressure hose for transporting the refrigerant used in the air conditioning system is exposed to a comparatively low temperature around 0xc2x0 C. while the air conditioning system is operated. On the other hand, while the air conditioning system is not operated, the hose is exposed to the ambient temperature, that is, the temperature of the environment in which the hose is disposed, e.g., a comparatively high temperature around 80xc2x0 C. in an engine room of the automotive vehicle. Accordingly, the hose is required to exhibit an excellent vibration absorbing characteristic over a wide temperature range, i.e., at a considerably low temperature and at a considerably high temperature. In view of the recent demands for reducing the size of the engine room and increasing the output of the engine of the automotive vehicle, the refrigerant transporting hose is likely to be used under a high-temperature condition. Further, it is desirable to eliminate the need of the maintenance of the hose. Thus, the refrigerant transporting hose used in the air conditioning system of the automotive vehicle is required to exhibit a high degree of resistance to heat and a high degree of vibration absorbing characteristic, even in the high-temperature condition.
The conventional rubber hose having the laminar structure described above, however, is not satisfactory for the following reasons when it is used in a condition wherein the hose is subjected to the vibrations, e.g., when the hose is used as the refrigerant transporting hose. Namely, the conventional rubber hose is not capable of exhibiting a high degree of vibration absorbing characteristic over the wide temperature range from the considerably low temperature to the considerably high temperature since the material characteristics of the hose greatly change with changes of the temperature in which the hose is used. Accordingly, the conventional rubber hose is not capable of reducing the noise due to its vibrations.
As a result of an extensive study made by the inventors of the present invention to produce a hose capable of exhibiting high degrees of flexibility and vibration absorbing characteristic over a wide temperature range from a considerably low temperature to a considerably high temperature, it was found that it is desirable that the hose has a low value of storage Young""s modulus (Exe2x80x2) and a high value of loss factor (tan xcex4) and that the hose is formed of a material which assures reduced temperature dependency of those physical properties, i.e., the storage Young""s modulus and the loss factor. The inventors found that an EPM material consisting of ethylene-propylene copolymer is excellent in terms of the storage Young""s modulus and the loss factor, and that the EPM material assures reduced temperature dependency of those physical properties. Accordingly, the rubber hose wherein the outer rubber layer of its laminar structure is formed of the EPM material exhibits a good vibration absorbing characteristic, and the temperature dependency of its vibration absorbing characteristic is significantly reduced.
It is therefore an object of the present invention to provide a rubber hose which exhibits high degrees of flexibility and vibration absorbing characteristic over a wide range of the temperature in which the hose is used, i.e., at a considerably low temperature and at a considerably high temperature, the rubber hose being used, in particular, as a refrigerant transporting hose in which the temperature dependency of its vibration absorbing characteristic is significantly reduced.
The above-indicated object of the present invention may be achieved according to a principle of the invention, which provides a vibration absorbing rubber hose having a laminar structure including an inner rubber layer, a reinforcing layer, and an outer rubber layer, which layers are laminated integrally with one another in the order of description in a radially outward direction of the rubber hose, wherein the inner rubber layer is formed of a butyl rubber material and/or a halogenated butyl rubber material while the outer rubber layer is formed of an EPM material consisting of ethylene-propylene copolymer.
In the vibration absorbing rubber hose constructed as described above, the outer rubber layer of its laminar structure is formed of the EPM material which is excellent in terms of not only flexibility but also storage Young""s modulus and loss factor, and which assures reduced temperature dependency of those physical properties. Accordingly, the present vibration absorbing rubber hose assures high degrees of flexibility and vibration absorbing characteristic over a wide temperature range from a considerably low temperature to a considerably high temperature. Therefore, the rubber hose is prevented from vibrating, so that the noise due to the vibration of the hose can be effectively minimized or prevented.
In one preferred form of the present invention, the EPM material is vulcanized to provide the outer rubber layer, by using a peroxide as a vulcanizing agent in the presence of a co-crosslinking agent whose molecular weight is not smaller than 200 or which has three or more functional groups. In the present rubber hose whose outer rubber layer is constituted by the vulcanized EPM rubber which is obtained by vulcanizing the EPM material with the peroxide in the presence of the co-crosslinking agent or coagent described above, the deterioration of the physical properties exhibited by the vulcanized EPM rubber are effectively prevented even when the EPM material for the outer rubber layer is laminated on and vulcanized with different kinds of rubber materials to provide the laminar structure of the hose. Accordingly, the present rubber hose advantageously exhibits the desired properties provided by the EPM material.
In another preferred form of the present invention, the EPM material which has been vulcanized with the peroxide in the presence of the co-crosslinking agent to provide the outer rubber layer has a characteristic which satisfies the following formulas:
Exe2x80x2(xe2x88x9220xc2x0 C.)xe2x89xa61.0xc3x97109 dyn/cm2
[Exe2x80x2(100xc2x0 C.)/Exe2x80x2(xe2x88x9220xc2x0 C.)]xe2x89xa70.1
tan xcex4(100xc2x0 C.)xe2x89xa70.10
[tan xcex4(100xc2x0 C.)/tan xcex4(xe2x88x9220xc2x0 C.)]xe2x89xa70.3
wherein,
Exe2x80x2(xe2x88x9220xc2x0 C.): storage Young""s modulus in an atmosphere at a temperature of xe2x88x9220xc2x0 C.
tan xcex4(xe2x88x9220xc2x0 C.): loss factor in an atmosphere at a temperature of xe2x88x9220xc2x0 C.
Exe2x80x2(100xc2x0 C.): storage Young""s modulus in an atmosphere at a temperature of 100xc2x0 C.
tan xcex4(100xc2x0 C.): loss factor in an atmosphere at a temperature of 100xc2x0 C.
The present arrangement provides the intended vibration absorbing rubber hose which exhibits high degrees of flexibility and vibration absorbing characteristic over the wide range of temperature in which the rubber hose is used.
In still another preferred form of the present invention, the vibration absorbing rubber hose is used as a refrigerant transporting hose for transporting a refrigerant. Described in detail, the present vibration absorbing rubber hose having the laminar structure whose inner rubber layer is formed of the butyl rubber material and/or the halogenated butyl rubber material can be used as a practically satisfactory refrigerant transporting hose which assures a considerably low degree of permeation of the refrigerant therethrough. The refrigerant which is transported by the present rubber hose preferably contains 1,1,1,2-tetrafluoroethane (HFC134a:CF3CH2F) as a major component.